The present invention relates to a method for controlling a temperature, and more particularly, to a temperature control method that is suitable for controlling a temperature of air within a chamber called a "freezing container" in which articles to be transported are accommodated.
One example of a temperature control method in a freezing container in the prior art will be explained with reference to FIG. 1. In this figure, a gaseous refrigerant discharged from a refrigerant compressor (1) enters a condenser (2) in which the refrigerant is cooled and condenses into liquid, thereafter it enters a restrictor (3) in which it expands adiabatically, then it enters an evaporator (4) in which the refrigerant itself is heated as a result of cooling the air circulating through the chamber accommodating articles and evaporates into gas, and the refrigerant returns to the compressor (1) in a gaseous state. By opening a valve (5), a part of the gaseous refrigerant discharged from the compressor (1) detours the condenser (2) and the restrictor (3) and enters the evaporator (4) without radiating heat, hence an air cooling capacity in the evaporator (4) can be reduced, and therefore, the air cooling capacity can be decreased or increased by increasing or decreasing, respectively, the degree of opening of the valve (5).
A temperature of a return air (6) from the chamber accommodating articles is detected by a temperature detector (8), and a temperature of a blow-out air (7) which has been cooled by the evaporator (4) is detected by a temperature detector (9). The detection temperature detected by the temperature detector (8) is input to temperature detector abnormality determining means (13), in which the detection temperature is compared with an abnormal condition range set in temperature detector abnormal condition setting means (14). In the event that the detection temperature falls within this abnormal condition range, the temperature detector abnormality determining means (13) determines that the temperature indicated by the detector (8) is abnormal, and makes the result of this determination indicated on indicator means (19). At the same time the determining means (13) instructs temperature detector selecting means (15) not to use the detection temperature of the temperature detector (8) for control purposes. Likewise, the detection temperature detected by the temperature detector (9) is input to temperature detector abnormality determining means (12), in which the detection temperature is compared with an abnormal condition range that is input from the temperature detector abnormal condition setting means (14). In the event that the detection temperature falls within this abnormal condition range, the temperature indicated by the detector abnormality determining means (12) determines that the temperature detector (9) is abnormal, and calls indicator means (18) to indicate the result of this determination. At the same time, the determining means (12) instructs the temperature detector selecting means (15) not to use the detection temperature of the temperature detector (9) for control purposes. In the case where neither of the temperature detectors (8) and (9) is abnormal, the temperature detector selecting means (15) receives a set temperature preset in the temperature setting means (16), and depending upon this set temperature, it selects a detection temperature of which one of the temperature detectors (8) and (9) should be used for control purposes. In addition, the set temperature preset in the temperature setting means (16) is input to thermostat selecting means (20). The thermostat selecting means (20) then selects either a cold storage thermostat (25) or a freezing thermostat (22), depending upon the set temperature.
In FIG. 6 is shown an operation instructed by the cold storage thermostat (25). Operation mode (A) indicates a strong cooling operation by switching ON the compressor (1); operation mode (B) indicates a weak cooling operation in which regulation of a degree of opening of the valve (5) is effected while operating the compressor (1); operation mode (C) indicates a weak heating operation by passing a current through a heater (33), and operation mode (D) indicates a strong heating operation by passing currents through both the heater (33) and a heater (34).
Assuming now that the temperatures indicated by both temperature detectors (8) and (9) have been determined not to be abnormal in the temperature detector abnormality temperature means (13) and (12), respectively, and a temperature corresponding to the cold storage condition has been set in the temperature setting means (16). Then in response to signals issued from these means, the temperature detector selecting means (15) selects the use of the detection temperature of the temperature detector (9) for control purposes according to the set temperature corresponding to the cold storage condition. The thermostat selecting means (20) also responds to a signal issued from the temperature setting means (16) and selects the use of the cold storage thermostat (25) according to the set temperature corresponding to the cold storage condition. Then, the detection temperature of the selected temperature selector (9) is supplied from the temperature detector selecting means (15) to a deviation calculator (17). At the same time, the set temperature preset in the temperature setting means (16) passes through a set value correcting means (23) without being corrected therein and is supplied to the deviation calculator (17); in this deviation calculator (17), the detection temperature of the temperature detector (9) and the set temperature are compared so as to calculate the deviation therebetween. This deviation is input to an operation instructor (11), in which the deviation is compared with an operation pattern input from the cold storage thermostat (25), and an operation mode selected according to the result of the comparison is instructed from the operation instructor (11). Assuming now that the detection temperature of the temperature detector (9) is 4.degree. C. and the set temperature is 0.degree. C., then a deviation of +4 deg. is calculated in the deviation calculator (17) and is input to the operation instructor (11). In the operation instructor (11), the deviation of +4 deg. is compared with the operation pattern of the cold storage thermostat (25) as shown in FIG. 6 hence, the operation mode (A), corresponding to the deviation of +4 deg. is instructed from the operation instructor (11), and the operation of the compressor (1) is started. As a result of the operation of the compressor (1), air is cooled by the evaporator (4) resulting in the lowering of the air temperature. When the detection temperature of the temperature detector (9) becomes 0.degree. C. and the deviation from the set temperature 0.degree. C. becomes equal to zero, then a transfer to an operation according to the operation mode (B) is instructed from the operation instructor (11), so as to cause the deviation of the detection temperature from the set temperature to become equal to zero. The control is effected by opening and closing the valve (5) while operating the compressor (1). If a thermal load changes in excess of a controllable range of this operation mode, and if the detection temperature becomes -1.degree. C. which is lower than the set temperature 0.degree. C. by 1 deg., then the operation instructor (11) instructs the transfer to the operation mode (C), and so, a weak heating operation is carried out by passing a current through the heater (33). Naturally, the temperature of the blow-out air (7) would rise. However, if the deviation of the detection temperature from the set temperature 0.degree. C. is still continuously kept less than zero due to the lowering of the ambient air temperature, for example, then the operation instructor (11) instructs the transfer to the operation mode (D), and so, a strong heating operation is carried out by passing currents through the heater (33) and the heater (34). When the detection temperature is rising and when the deviation has reached +3 deg., the operation is transferred from the operation mode (D) to the operation mode (C); when the deviation has become +2 deg., the operation is transferred from the operation mode (C) to the operation mode (B), and when the deviation has reached +3 deg., the operation is transferred from the operation mode (B) to the operation mode (A). In the case where the temperature indicated by both temperature detectors (8) and (9) are determined not to be abnormal and a temperature corresponding to a freezing condition is set in the temperature setting means (16), then a deviation of the detection temperature of the temperature detector (8) from the set temperature is compared with an operation pattern (not shown) of the freezing thermostat (22). An operation mode is then selected according to the result of the comparison, said selection being instructed from the operation instructor (11).
The following description is made for the case where the temperature indicated by the detector (9) has been determined to be abnormal and a temperature 0.degree. C. corresponding to the cold storage condition has been set in the temperature setting means (16).
In this case, the temperature detector selecting means (15) does not select the detection temperature of the temperature detector (9) which corresponds to the set temperature 0.degree. C., but selects the use of the detection temperature of the temperature detector (8) for control purposes, and so, the latter detection temperature is input to the deviation calculator (17). In this instance, the set temperature preset in the temperature setting means (16) is input to the set value correcting means (23). In correcting means (23), the set temperature is corrected so as to be raised by a predetermined fixed amount that is equivalent to the temperature difference between the temperature of the return air (6) and the temperature of the blow-out air (7) upon a cooling operation, for example, by 3 deg. The corrected set temperature is then input to the deviation calculator (17). In the deviation calculator (17), the deviation of the detection temperature of the temperature detector (8) from the corrected set value is calculated. This deviation is input to the operation instructor (11), in which the deviation is compared with an operation pattern of the cold storage thermostat (25). An operation mode selected on the basis of the result of this comparison is instructed from the operation instructor (11).
It is to be noted that in the case where the temperature indicated by the detector (8) has been determined to be abnormal, the control operation is not affected at all upon cold storage, and upon freezing, except for the fact that control is effected by making use of the temperature detector (9). In the set value correcting means (23), the set temperature is corrected so as to be lowered by a predetermined fixed amount, for example, by 2 deg., and the control operation is substantially identical to that described above with respect to the other points. Accordingly, a further description thereof has been omitted.
In the above-described temperature control method in the prior art, in the event that either one of the temperature indicated by the detectors has been determined to be abnormal, the temperature control can be achieved by making use of the temperature of the other temperature detector which is normal. However, in this case, since the set temperature preset in the temperature setting means (16) is corrected by a fixed amount equivalent to the temperature difference between the temperature of the return air (6) and the temperature of the blow-out air (7) upon cooling, it is impossible to always carry out proper correction. For instance, in the case of the carrying out of a heating operation, there is a disadvantage that in if the above-mentioned correction is effected, then the target temperature may possibly become too high or too low.